This invention relates generally to the field of intraocular lenses (IOL) and, more particularly, to anterior chamber phakic IOLs.
The human eye in its simplest terms functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of a crystalline lens onto a retina. The quality of the focused image depends on many factors including the size and shape of the eye, and the transparency of the cornea and the lens.
The optical power of the eye is determined by the optical power of the cornea and the crystalline lens. In the normal, healthy eye, sharp images are formed on the retina (emmetropia). In many eyes, images are either formed in front of the retina because the eye is abnormally long (axial myopia), or formed in back of the retina because the eye is abnormally short (axial hyperopia). The cornea also may be asymmetric or toric, resulting in an uncompensated cylindrical refractive error referred to as corneal astigmatism. In addition, due to age-related reduction in lens accommodation, the eye may become presbyopic resulting in the need for a bifocal or multifocal correction device.
In the past, axial myopia, axial hyperopia and corneal astigmatism generally have been corrected by spectacles or contact lenses, but there are several refractive surgical procedures that have been investigated and used since 1949. Barraquer investigated a procedure called keratomileusis that reshaped the cornea using a microkeratome and a cryolathe. This procedure was never widely accepted by surgeons. Another procedure that has gained widespread acceptance is radial and/or transverse incisional keratotomy (RK or AK, respectively). Recently, the use of photablative lasers to reshape the surface of the cornea (photorefractive keratectomy or PRK) or for mid-stromal photoablation (Laser-Assisted In Situ Keratomileusis or LASIK) have been approved by regulatory authorities in the U.S. and other countries. All of these refractive surgical procedures cause an irreversible modification to the shape of the cornea in order to effect refractive changes, and if the correct refraction is not achieved by the first procedure, a second procedure or enhancement must be performed. Additionally, the long-term stability of the correction is somewhat variable because of the variability of the biological wound healing response between patients.
Several companies are investigating implantable anterior chamber phakic IOLs, including Bausch and Lomb""s NuVita and Model ZB5M lenses, and the Artisian iris claw lens by Ophtec BV. These and other anterior chamber phakic lenses are described in U.S. Pat. Nos. 5,071,432 (Baikoff), 5,192,319 (Worst), 5,300,117 (Baikoff, et al.), 5,928,282 (Nigam) and PCT Publication No. WO 98/56315. The clinic experience with commercially available anterior chamber phakic lenses has not been entirely satisfactory does to difficult implantation techniques and clinical complications such as endothelial cell loss and pupil ovaling.
Prior art iris-fixated anterior chamber lenses, such as those described in U.S. Pat. No. 6,152,959 (Portney) and U.S. Pat. No. 5,192,319 (Worst) which is commercially available as the Artisan lens from Ophtec BV are made from polymethyl methacrylate (PMMA), which is a relatively hard thermoplastic and not considered to be a foldable material. The hardness of the iris fixating pincers arms makes it difficult to gather enough iris tissue within the pincer arms to hold the lens because the surgeon must pull the relatively rigid arms apart while simultaneously gather iris tissue into the gap between the arms. In addition, the rigidity of PMMA requires that the gap between the pincer arms in the relaxed state be relatively large so as to avoid injuring the iris. See, for example at column 2, lines 66-67 of Portney xe2x80x2959 where the preferred pincer gap is described as being between 0.05 mm and 0.25 mm. Such a large gap requires that a great deal of iris tissue be gather within the gap in order to hold the lens stable on the iris.
Therefore, a need continues to exist for a safe, biocompatible and easily fixated anterior chamber phakic intraocular lens.
The present invention improves upon the prior art by providing an anterior chamber phakic lens made from an elastomeric, foldable, highly biocompatible material. The lens has a generally circular optic and integrally formed plate-style haptics, the haptics containing an opening into which project a pair of pincer arms. The pincer arms are sized and shaped so as to pull away from each other when the lens is folded, and are draw back toward each other when the folded lens is released and allowed to return to its unfolded state. Such movement allows the pincers to gather a small section of the iris so as to hold the lens in place.
Accordingly, one objective of the present invention is to provide a safe and biocompatible intraocular lens.
Another objective of the present invention is to provide a safe and biocompatible intraocular lens that is easily fixated on the iris.
Still another objective of the present invention is to provide a safe and biocompatible intraocular lens that is stable in the anterior chamber.
These and other advantages and objectives of the present invention will become apparent from the detailed description and claims that follow.